Study of sowing method and fertilizer applied to green manure crops to increase the yield of corn

Experiment was conducted to find out the promising species of green manure crops, the suitable method of sowing their seeds, and the optimum rate of a complete fertilizer applied to the manure crop to increase the yield of corn grown on a black clayey soil (very fine, montmorillonitic, isohyperthermic, Typic Pellusterts). The split-split plot design with 3 replications was employed in the experiment. Two green manure crops: cowpea (Vigna unguiculata), and bonavist (Lablab purpureus) were treated as the main plot: 2 methods, of sowing the manure crop: seed broadcast, and seed drill, as the subplot: and 5 application rates of 15-15-15-fertilizer at 0, 15, 30, 45 and 60 kg/rai as the sub-subplot. At 60 days after emergence (DAE), the green manure legumes were plowed under the soil. Corn (var. Nakorn Sawan 1) was subsequently planted in the plots as the main crop after 21 days of the legume-soil incorporation. However, no fertilizer was supplemented to the corn. The results showed that the mean height and the mean fresh weight of the cowpea at the time of soil incorporation, were greater than those of the bonavist. But there were no significant difference in the height and the fresh weight of the two legume plants sown by seed broadcast and seed drill. However, the application of the 15-15-15-fertilizer at 15 kg/rai and higher rates resulted in the greater height, and fresh weights of the legume plants than that at 0 kg/rai. But there were no differences in the plant heights, and fresh weights among those different rates of fertilizer application. The mean height at 30 DAE and the mean weight of the corn stubble obtained from the cowpea green manure were higher than those from the bonavist. Unlikely, the mean grain yield nourished by either the cowpea or bonavist did not show any significant difference. Also, the method of planting the manure legumes, as well as the different rates of the 15-15-15 fertilizer applied to the legumes, did not affect the mean height and the mean weight of the corn stubbles. But the fertilizer applied to the manure legumes at 15 kg/rai resulted in the higher corn yield than that at 0/kg/rai. However, those application rates (15, 30, 45 and 60 kg/rai) did not show the significant differences in the corn yield. This inferred that the manure legumes applied with 15 kg/rai of 15-15-15 fertilizer be sufficient to increase the yield of corn.